Noncontact lifetime characterization technique for LWIR HgCdTe using transient millimeter-wave reflectance

A noncontact, noninvasive lifetime characterization technique for measuring the excess carrier lifetime in long wavelength infrared (LWIR) Hg1-xCdxTe (x approximately equals 0.20-0.225) using transient millimeter-wave (90 GHz) reflectance is presented. Excess carrier lifetime results for both p-type (vacancy-doped >= 1 X 1016 cm-3) and n-type (annealed <= 1x1015 cm-3 epilayer material are given. The lifetimes in vacancy-doped p-type HgCdTe are short, i.e., approximately 25 ns at 80 K, thereby requiring a short-pulsed laser source and high-bandwidth electronics in the lifetime test system. The lifetime test system employs either YAG (1.06 micrometers ) or CO2 (9-11 micrometers ) pulsed laser excitation. Lifetime results for both frontside and backside laser illumination of the epilayer HgCdTe are presented. The effect of surface recombination of lifetime and reflected millimeter-wave signal amplitude is discussed.